The maximum pressure that granite rock can withstand is 2.0 × 108 N m-2. Above this pressure, the rock begins to flow like a liquid.

Question 30

The maximum pressure that granite rock can withstand is 2.0 × 10⁸ N m^-2. Above this pressure, the rock begins to flow like a liquid. The density of granite is 2.7 × 10³ kg m^-3.

What would be the height of a pure granite mountain whose base is just beginning to flow?

A 3.8 × 10³ m           B 7.6 × 10³ m           C 3.7 × 10⁴ m           D 7.4 × 10⁴ m

Reference: Past Exam Paper – June 2015 Paper 12 Q20

Solution:

Answer: B.

Maximum pressure that the rock can withstand = 2.0×10⁸ N m^-2.

This pressure is caused by a height h of granite.

Pressure P = hρg

Height h = P / ρg

Height h = (2.0×10⁸) / (2.7×10³ × 9.81)

Height h = 7.6×10³ m